Regulation of skin blood flow in man includes both thermal (internal temperature, skin temperature) and non-thermal (posture, exercise) reflexes. The efferent arms of these reflexes include separate vasoconstrictor and vasodilator neural elements, the latter being postulated by some to be secondary to the activation of sweat glands. This project is a continuation of work aimed at furthering our understanding of the regulation of skin blood flow when non-thermal reflexes for cutaneous vasoconstriction are in competition with thermal reflexes for vasodilation. Experiments are designed to test whether exercise or the upright posture alter the sensitivity (change of skin blood flow per unit change in internal temperature) or the threshold for the onset of thermally-induced cutaneous vasodilation. Major emphasis is placed on this competitive interaction during exercise. Specific questions posed include: a) Are the levels or work or of skin temperature determinants of the upper level of skin blood flow during exercise? b) Does the cutaneous vasoconstriction accompanying the onset of exercise become more pronounced with rising internal temperature? c) Do vasomotor and sudomotor adjustments accompanying exercise onset indicate a shift in the set point for thermoregulation? d) Is the cutaneous vasomotor response to isometric exercise abolished or modified by simultaneous heat stress? e) Is the control of sweating altered by non-thermal reflexes in a manner similar to alterations in skin blood flow? f) Does skin blood flow as measured in the forearm reflect cutaneous vasomotor changes over the majority of the body surface? Answers to these questions should clarify basic schemes of control of the cutaneous circulation allowing more rational predictions as to the circulatory consequences of the combination of heat stress and exercise in the presence of cardiovascular disease.